The present invention relates to an improved far-infrared electric heater, and more particularly to a far-infrared electric heater including an electric heating coil wound about an inner element formed from sintered quartz and far-infrared optical material and then covered with an outer tube. An inner surface of the outer tube and/or an outer surface of the inner element can be provided with continuous teeth to achieve optimal heating effect.
It has been known that far-infrared heaters are widely employed in general domestic appliances, such as electric ovens, radiant heaters, microwave ovens, etc. The employment of far-infrared heaters can generally have the advantages of fast and even heating, lower consumption of energy, and superior heating effect. FIGS. 1 and 2 illustrate a conventional far-infrared heater that has been currently widely used in an electric oven. As shown, the far-infrared heater includes an electric heating coil 1 set in an outer tube 2 which serves as a supporter and insulator for the heating coil 1. Generally, the outer tube 2 is made of high-temperature resistant and insulating materials, such as quartz, ceramic enamel, or other ceramic materials. Moreover, far-infrared optical paint 3 is sprayed over circumferential surface of the outer tube 2. The electric heating coil 1 spirally extends with two ends thereof connected to a power source. When the heating coil 1 is supplied with a current and heated, it produces radiant energy which passes the far-infrared optical paint 3 over the circumferential surface of the outer tube 2 and is refracted to produce far-infrared sources. The produced far-infrared rays are further reflected by an aluminum-plated inner case of the electric oven in which the far-infrared heater is installed, so that food in the electric oven is subjected to the far-infrared rays from different directions in the oven and can be evenly heated and cooked within a shortened time.
Generally, there are three ways to combine the far-infrared optical paint 3 with the outer tube 2: 1) the far-infrared optical paint is sprayed over the circumferential surface of a quartz tube, 2) the far-infrared optical paint is sprayed over the circumferential surface of a ceramic enamel tube, and 3) the far-infrared optical paint is mixed with ceramic powder and the mixture is sintered to form the outer tube 2. However, following problems with the outer tube 2 formed from these three ways can be found from long-term observation over the use of such outer tube 2 in the conventional far-infrared heater:
A. For a quartz tube sprayed with far-infrared optical paint:
a. The sprayed far-infrared optical paint tends to be scraped off during transportation or assembling and makes the quartz tube looking ugly; PA1 b. The sprayed far-infrared optical paint tends to peel off when the quartz tube is heated at high temperature and therefore contaminates food being cooked; PA1 c. The far-infrared optical paint is not well pervious to light that results in slow raising of temperature and prolonged time of baking or roasting, as well as low working efficiency and higher consumption of energy; PA1 d. The far-infrared optical paint forms uneven surface on the outer tube. Grease from the cooked food tends to attach to and cumulate on the uneven surface and is not easily removed therefrom after the far-infrared heater has been used for a long time. The grease-attached far-infrared heater looks ugly and dirty, and will adversely affect the radiation of the far-infrared rays; and PA1 e. When the outer tube 2 is broken, the spirally extended heating coil 1 is not supported and is easily exposed to the open air to dangerously shock a user. PA1 a. The sprayed far-infrared optical paint tends to be scraped off during transportation or assembling and makes the ceramic enamel tube looking ugly; PA1 b. The sprayed far-infrared optical paint tends to peel off when the ceramic enamel tube is heated at high temperature and therefore contaminates food being cooked; PA1 c. The ceramic enamel tube sprayed with the far-infrared optical paint is even inferior in its perviousness to light than the quartz tube and therefore has even slower raising of temperature and needs longer time of baking or roasting. The efficiency of energy conversion is even lower and the consumption of energy is even higher than the quartz tube; PA1 d. The far-infrared optical paint forms uneven surface. Grease from the cooked food tends to attach to and cumulate on the uneven surface and is not easily removed therefrom after the far-infrared heater has been used for a long time. The grease-attached far-infrared heater looks ugly and dirty, and will adversely affect the radiation of the far-infrared rays; and PA1 e. When the outer tube 2 is broken, the spirally extended heating coil 1 is not supported and is easily exposed to the open air to dangerously shock a user. PA1 a. Like the ceramic enamel tube, this type of ceramic tube is even inferior in its perviousness to light than the quartz tube and therefore has even slower raising of temperature and needs longer time of baking or roasting. The efficiency of energy conversion is even lower and the consumption of energy is even higher than the other two types of outer tubes; PA1 b. The far-infrared optical paint forms uneven surface. Grease from the cooked food tends to attach to and cumulate on the uneven surface and is not easily removed therefrom after the far-infrared heater has been used for a long time. The grease-attached far-infrared heater looks ugly and dirty, and will adversely affect the radiation of the far-infrared rays; and PA1 c. When the outer tube 2 is broken, the spirally extended heating coil 1 is not supported and is easily exposed to the open air to dangerously shock a user.
B. For a ceramic enamel tube sprayed with far-infrared optical paint:
C. For a ceramic outer tube containing far-infrared optical material through sintering: